The present invention relates to slurry feeding apparatus and method for use in a chemical/mechanical polishing (CMP) process of a wafer.
In recent years, the surface of a semiconductor wafer is often planarized by a CMP technique to ensure sufficient uniformity for an interlevel dielectric film, for example, during the manufacturing process of transistors on the substrate. The CMP process is performed using a kind of slurry, where fumed or colloidal silica is dispersed as abrasive grains in an alkaline solution of ammonium, for example.
FIG. 8 illustrates a cross section of a known (polishing) slurry feeding apparatus F1 as disclosed in Japanese Laid-Open Publication No. 10-15822.
As shown in FIG. 8, the slurry feeding apparatus F1 includes tank 101, delivery pipe 102 with a pump 104, flow rate control valve 103, feeding nozzle 110 and stirrer 106. Polishing slurry 109 is stored in the tank 101 and delivered through the delivery pipe 102 from the tank 101 to a CMP polisher (not shown). The flow rate control valve 103 is provided in the middle of the pipe 102 downstream of the pump 104. The feeding nozzle 110 is attached to the end of the pipe 102 for dripping the slurry 109 onto a polishing pad (not shown) of the polisher. And the stirrer 106 with a propeller is used for stirring the slurry 109. A circulation pipe 105 is further provided as a branch from the delivery pipe 102 upstream of the valve 103 to circulate the slurry 109 by feeding the slurry 109 back to the tank 101 therethrough. A heater 107 is further provided on the bottom of the tank 101 to regulate the temperature of the slurry 109 within the tank 101. The temperature of the heater 107 is in turn regulated by a heater temperature controller 108. In polishing a wafer, the opening of the valve 103 is adjusted and a predetermined amount of the slurry 109 is sucked up from the tank 101 using the pump 104 and then dripped onto the polishing pad through the feeding nozzle 110. The remainder of the slurry 109 is recovered to the tank 101 through the circulation pipe 105. On the other hand, while the polishing process is not performed, the valve 103 is closed and all the slurry 109 is recovered to the tank 101, thereby circulating the slurry 109 without delivering it.
As for colloidal silica, the primary grains thereof have a tiny size of 20 to 30 nm. But in the polishing slurry 109, a certain number of primary silica grains coagulate to form secondary grains with a size of 100 to 200 nm. As for fumed silica on the other hand, the grain size thereof is 100 to 200 nm from the beginning (i.e., when they are prepared). Thus, it is generally believed that these secondary grains with a grain size of 100 to 200 nm actually contribute to the polishing process.
Nevertheless, if an excessive number of abrasive grains coagulate together to form grains with a size as large as about 500 nm or more, then micro-scratches are possibly made on the object being polished.
Thus, the conventional slurry feeding apparatus F1 always circulates the polishing slurry 109 and stirs the slurry 109 up with the propeller, thereby suppressing the sedimentation and coagulation of the abrasive grains in the slurry 109.
FIG. 10 illustrates a cross section of a coupling generally provided for the piping where the slurry flows in a conventional slurry feeding apparatus. By using couplings in various shapes for the corner or linear portions, piping can be formed in a complicated shape and the cross-sectional area of the piping and the overall size of the slurry feeding apparatus can be both reduced.
It is known that the excessively promoted coagulation of the abrasive grains (e.g., with a grain size of more than about 500 nm) not only causes micro-scratches on the object being polished but also decreases the polishing rate.
FIG. 9 is a graph illustrating, in comparison, respective polishing rates of Slurry 1 and 2 with mutually different concentrations of solid content (abrasive grains) in accordance with results of experiments carried out by the present inventors. As can be seen from FIG. 9, although the solid content concentration of Slurry 1 is only 1% lower than that of Slurry 2, the polishing rate attained by Slurry 1 is considerably lower than that attained by Slurry 2. Such a decrease in solid content concentration could result from the sedimentation of abrasive grains with an excessively increased size in the tank. Accordingly, it is critical to prevent the size of abrasive grains from increasing excessively in order to obtain an appropriate polishing rate.
To suppress the coagulation of abrasive grains, the conventional slurry feeding apparatus has the following draw-backs.
Firstly, the increase in size of abrasive grains in the slurry 109 cannot be suppressed sufficiently only by stirring the the slurry 109 up using the stirrer 106 with a propeller as shown in FIG. 8.
Secondly, the slurry 109 is likely to form puddles here and there in the regions Rg of the coupling where two pipes of the piping are joined together in the slurry feeding apparatus F1. This is because there are many gaps and level differences between these pipes in the region Rg as shown in FIG. 10. As a result, the excessive coagulation of the abrasive grains is possibly promoted.
Thirdly, the solidified contents of the slurry 109 are likely to deposit on the inner walls of the tank 101 as the level of the slurry solution changes in the tank 101. And the solidified slurry 109 once deposited will collapse within the tank 101 to increase the size of the grains coagulated.
Since the size of the abrasive grains is excessively increased in this manner, the micro-scratches are made on the object being polished and the polishing rate thereof decreases or becomes inconstant.
An object of the present invention is reducing the number of micro-scratches made on the object being polished and attaining an intended polishing rate by suppressing the excessive increase in size of the abrasive grains. Exemplary measures include: improving slurry stirring and circulating methods; eliminating gaps and level differences from the inside of piping; and preventing the solidified slurry from being deposited on the inner walls of the tank.
A first exemplary slurry feeding apparatus according to the present invention is adapted to feed polishing slurry to a chemical/mechanical polisher. The apparatus includes: a container for storing the slurry therein; a first nozzle for sucking the slurry up from the container; a second nozzle for recovering the slurry back to the container; a third nozzle for dripping the slurry in the polisher; a first pipe, which is connected to the first and third nozzles for delivering the slurry to the polisher; a second pipe, which is connected to the second nozzle and the first pipe for bypassing at least part of the slurry flowing through the first pipe from the third nozzle and then recovering that part of the slurry back to the second nozzle; a control valve for regulating the flow rate of the slurry, which is now flowing through the first pipe and will be supplied to the third nozzle and the second pipe; a pump, which is provided for at least one of the first and second pipes for making the slurry flow with a pressure applied; and control means for operating the pump continuously while the polisher is operating and intermittently while the polisher is idling.
According to the first apparatus, it is possible to minimize the number of excessively large-sized abrasive grains, which usually result from their collision in the slurry due to the pressure applied from a pump.
A second exemplary slurry feeding apparatus is also adapted to feed polishing slurry to a chemical/mechanical polisher. The apparatus includes: a container for storing the slurry therein; a first nozzle for sucking the slurry up from the container; a second nozzle for recovering the slurry back to the container; a third nozzle for dripping the slurry in the polisher; a first pipe, which is connected to the first and third nozzles for delivering the slurry to the polisher; a second pipe, which is connected to the second nozzle and the first pipe for bypassing at least part of the slurry flowing through the first pipe from the third nozzle and then recovering that part of the slurry back to the second nozzle; a control valve for regulating the flow rate of the slurry, which is now flowing through the first pipe and will be supplied to the third nozzle and the second pipe; and a pump, which is provided for at least one of the first and second pipes for making the slurry flow with a pressure applied. The first nozzle sucks up portion of the slurry that is located higher than the bottom of the container by a predetermined distance or more.
According to the second apparatus, it is possible to prevent abrasive grains of an excessively large size, which are sedimented easily on the bottom of the container, from being sucked up through the first nozzle and then delivered to the CMP polisher.
In one embodiment of the present invention, the first nozzle preferably sucks up portion of the slurry that is located higher than the bottom of the container by 5 centimeters or more.
In another embodiment, the end of the first nozzle may be cut away obliquely with respect to the axis thereof.
In an alternate embodiment, the end of the first nozzle may be closed, and the side of the first nozzle may be provided with a plurality of openings for sucking the slurry up therethrough.
In another alternate embodiment, the apparatus may further include a mechanism for adjusting the level of the first nozzle at the end thereof.
A third exemplary slurry feeding apparatus according to the present invention is also adapted to feed polishing slurry to a chemical/mechanical polisher. The apparatus includes: a container for storing the slurry therein; a first nozzle for sucking the slurry up from the container; a second nozzle for spraying the slurry into the container; a third nozzle for dripping the slurry in the polisher; a first pipe, which is connected to the first and third nozzles for delivering the slurry to the polisher; a second pipe, which is connected to the second nozzle and the first pipe for bypassing at least part of the slurry flowing through the first pipe from the third nozzle and then recovering that part of the slurry back to the second nozzle; a control valve for regulating the flow rate of the slurry, which is now flowing through the first pipe and will be supplied to the third nozzle and the second pipe; and a pump, which is provided for the second pipe for making the slurry flow with a pressure applied. The second nozzle sprays the slurry into the container from a position at a predetermined level over the bottom of the container.
According to the third apparatus, even if no stirrer such as a propeller is provided for the container, the slurry in the container can still be stirred up by being sprayed. Thus, it is possible to prevent the size of the abrasive grains from being increased overly due to the unwanted application of excessive energy from the propeller to the grains, for example.
In one embodiment of the present invention, the second nozzle may spray the slurry into the container from a position higher than the bottom of the container by 5 centimeters or less.
In an alternate embodiment, the second nozzle may have an opening with a reduced diameter at the end thereof. In such a case, the slurry can be sprayed at an increased velocity and therefore the slurry in the container can be stirred more effectively.
In another alternate embodiment, the apparatus may further include a mechanism for adjusting the level of the second nozzle at the end thereof.
In still another embodiment, a plurality of the second nozzles may be placed within the container.
A fourth exemplary slurry feeding apparatus according to the present invention is also adapted to feed polishing slurry to a chemical/mechanical polisher. The apparatus includes: a container for storing the slurry therein; a first nozzle for sucking the slurry up from the container; a second nozzle for recovering the slurry back to the container; a third nozzle for dripping the slurry in the polisher; a first pipe, which is connected to the first and third nozzles for delivering the slurry to the polisher; a second pipe, which is connected to the second nozzle and the first pipe for bypassing at least part of the slurry flowing through the first pipe from the third nozzle and then recovering that part of the slurry back to the second nozzle; a control valve for regulating the flow rate of the slurry, which is now flowing through the first pipe and will be supplied to the third nozzle and the second pipe; and a pump, which is provided for at least one of the first and second pipes for making the slurry flow with a pressure applied. Each of the first and second pipes is provided with no coupling at any intermediate point thereof.
According to the fourth apparatus, level differences and gaps involved with a coupling can be eliminated from the circulation pipe of the slurry. Thus, it is possible to prevent the size of abrasive grains from being increased excessively due to the slurry puddles.
A fifth exemplary slurry feeding apparatus according to the present invention is also adapted to feed polishing slurry to a chemical/mechanical polisher. The apparatus includes: a container for storing the slurry therein; a first nozzle for sucking the slurry up from the container; a second nozzle for recovering the slurry back to the container; a third nozzle for dripping the slurry in the polisher; a first pipe, which is connected to the first and third nozzles for delivering the slurry to the polisher; a second pipe, which is connected to the second nozzle and the first pipe for bypassing at least part of the slurry flowing through the first pipe from the third nozzle and then recovering that part of the slurry back to the second nozzle; a control valve for regulating the flow rate of the slurry, which is now flowing through the first pipe and will be supplied to the third nozzle and the second pipe; and a pump, which is provided for at least one of the first and second pipes for making the slurry flow with a pressure applied. The radius of curvature at a corner of the first and second pipes is 5 centimeter or more.
According to the fifth apparatus, the slurry puddles can be eliminated from the corners, thus preventing the size of abrasive grains from being increased excessively.
A sixth exemplary slurry feeding apparatus according to the present invention is also adapted to feed polishing slurry to a chemical/mechanical polisher. The apparatus includes: a hermetically sealed container for storing the slurry therein; a first nozzle for sucking the slurry up from the container; a second nozzle for recovering the slurry back to the container; a third nozzle for dripping the slurry in the polisher; a first pipe, which is connected to the first and third nozzles for delivering the slurry to the polisher; a second pipe, which is connected to the second nozzle and the first pipe for bypassing at least part of the slurry flowing through the first pipe from the third nozzle and then recovering that part of the slurry back to the second nozzle; a control valve for regulating the flow rate of the slurry, which is now flowing through the first pipe and will be supplied to the third nozzle and the second pipe; a pump, which is provided for at least one of the first and second pipes for making the slurry flow with a pressure applied; and means for externally supplying a wet ambient gas.
According to the sixth apparatus, a wet ambient can be created within the container. Thus, even if the slurry solution in the container has changed its level, it is possible to prevent any solidified slurry from being formed on the inner walls of the container.
A seventh slurry feeding apparatus according to the present invention is also adapted to feed polishing slurry to a chemical/mechanical polisher. The apparatus includes: a container for storing the slurry therein; a first nozzle for sucking the slurry up from the container; a second nozzle for recovering the slurry back to the container; a third nozzle for dripping the slurry in the polisher; a first pipe, which is connected to the first and third nozzles for delivering the slurry to the polisher; a second pipe, which is connected to the second nozzle and the first pipe for bypassing at least part of the slurry flowing through the first pipe from the third nozzle and then recovering that part of the slurry back to the second nozzle; a control valve for regulating the flow rate of the slurry, which is now flowing through the first pipe and will be supplied to the third nozzle and the second pipe; a pump, which is provided for at least one of the first and second pipes for making the slurry flow with a pressure applied; and sampling boards, which are attached to the container for extracting the slurry from the container for sampling purposes.
According to the seventh apparatus, the state of the slurry can always be monitored. Thus, chemical/mechanical polishing can be performed constantly.
In one embodiment of the present invention, the sampling boards are preferably attached to the container at upper, intermediate and lower portions thereof.
A first exemplary method according to the present invention is adapted to feed polishing slurry to a chemical/mechanical polisher. According to the first method, while the polisher is operating, the slurry is continuously circulated by extracting and delivering part of the slurry from a container, where the slurry is stored, to the polisher and by recovering the remaining slurry, which has not been delivered to the polisher, back to the container. On the other hand, while the polisher is idling, the slurry is circulated intermittently by recovering all of the slurry extracted back to the container.
The same effects as those attained by the first slurry feeding apparatus are also attainable by the first method.
A second exemplary method according to the present invention is also adapted to feed polishing slurry to a chemical/mechanical polisher. The slurry delivered from a container to the polisher is located higher than the bottom of the container by a predetermined distance or more.
The same effects as those attained by the second slurry feeding apparatus are also attainable by the second method.
A third exemplary method according to the present invention is also adapted to feed polishing slurry to a chemical/mechanical polisher. The slurry stored in a container is stirred up by spraying the slurry from a position higher than the bottom of the container by a predetermined distance with a pressure applied from a pump to the slurry in recovering the slurry back to the container.
The same effects as those attained by the third slurry feeding apparatus are also attainable by the third method.